The present invention relates to electromechanical transducers comprising a polymer element in which an electrical anisotropy has been introduced in the form of an excess electric charge or a dipolar orientation of the macromolecular chains. The invention relates more particularly to transducers such as loudspeakers, microphones, hydrophones, probes for echography, etc. in which the active structure is formed by at least a polymer film having been subjected to shaping of a nondevelopable type. Such a structure is self-supporting and requires no other support than peripheral securing. In practice, two modes of deformation are met with according as to whether the lamellar structure is homogeneous or heterogenous. The simplest example is that of a single film carrying metalizations on both its flat faces. Such a film, subjected to an energizing electric field, is deformed in three directions which are normal to its faces and two directions contained in its plane. In the case of a dimorphous structure formed from two films which adhere together, it is sufficient for the induced deformations to differ from one another for the whole to bend.
Apart from the thickness deformation, the other deformations depend on the stretching that the film has undergone during shaping. When the stretching is unidirectional, the deformations are greater in the stretching direction. On the contrary, in the absence of stretching or when the stretching is isotropic, the deformations are also isotropic.
In transducers using as active element a portion of a sphere, the peripheral securing opposes locally any circumferential deformation so that the movement depends largely on the buttressing effect which is exerted along the meridian lines. By replacing the peripheral securing with a passive annular undulating suspension, more freedom is given to the structure, but the vibrating-piston effect is still far from approaching the radial movement which characterizes a pulsating spherical surface. The result is a loss of efficiency and radiation fairly different from that of a pinpoint source.